The present invention relates to the reconstitution, upon arrival in a terminal, of messages conveyed in fragments through a packet-switched data transmission network in which these messages may be conveyed redundantly, by several independent transmission networks, in order to increase the security of their transportation.
A switched-packet data transmission network is constituted by a meshing of transmission lines and interconnection nodes linking geographically dispersed terminals that exchange messages with each other. The packets, which are formed by datagrams of variable length, travel asynchronously, in modulated form, on transmission lines. They are redirected in interconnection nodes through which they travel until they reach their destination. Their trajectory times are variable and depend on the congestion of the interconnection nodes when they cross these nodes. They comprise payload data constituting the payload of the network and service information enabling them to be routed within the network. It is not rare that a message to be transmitted is divided among several packets. In this case, the service information of the packets provides information on the fact that these packets belong to a same message and on their relative positions within this message to enable the reconstitution of the message at destination.
The invention more specifically relates to the reconstitution of messages fragmented in packets, upon the arrival of the packets at their destination, when the same message, for reasons of security, can be conveyed redundantly by several independent transmission networks, a same packet being capable of reaching the same terminal several times through different virtual channels or paths and at points in time that are close but distinct.
Hitherto, it has been the case that, when the same message, segmented into packets, is transmitted to a same terminal, by at least two independent transmission networks, the poor reception of one packet of the message on one of the networks leads to the rejection of all the packets of the message conveyed by this network. This prevents the reconstitution of a message through a combination of the packets conveyed by the two transmission networks when packets are badly conveyed on both networks, even if these cases where the packets are badly conveyed do not concern the same packets on both networks.